The leakage of air through a building envelope (i.e. air exfiltration and infiltration) causes several problems the more serious of which is the condensation of moisture present within the air as it passes through the building structure. The resulting condensation can cause surface staining of walls and ceilings, premature deterioration of the building structure and air leakage will cause an excessive energy loss. Consequently, building construction objectives and Canadian standards now require that effective air barrier systems, which avoid air leakage, be designed and used in the construction of new buildings and the retrofitting of existing buildings. Such standards which apply in Canada, but are not yet generally applied in other countries, are expected to be adopted elsewhere as construction technology advances and other countries recognize the need for such standards.
Where climatic conditions exist it is desirable to include in the design and construction of a building an effective air barrier to control the movement of humidity via air borne vapour in order to avoid any buildup of condensation and frost in the walls and roof. The properties of an effective air barrier are distinct from those of a vapour barrier, the purpose of vapour barriers being to prevent vapour diffusion. Vapour diffusion is determined by the porosity of a material, whereas an air barrier is evaluated by the rate of air leakage through it caused by holes in the air barrier or lack of continuity between different air barrier materials when installed (such as a discontinuity between the roofing membrane and an air barrier membrane). However, it is preferable, if possible, to combine both of these elements in one component. It is to be noted also that certain construction materials which were once deemed to be efficient air barriers between environments, such as concrete walls, are no longer satisfactory to meet current Canadian building requirements for air barriers. Although a perfectly poured test sample of concrete would test satisfactorily as an air barrier, the discontinuities and installation flaws of a poured concrete wall render such a wall unacceptable as an air barrier.
For this reason air barrier membranes are now installed over concrete walls. The term "air barrier" used herein means the building elements (and parts thereof) forming a building envelope which, to meet Canadian standards, must be effective to prevent air leakage therethrough at standardized pressure differential levels across the air barrier. (The term "air barrier" herein is not intended to refer simply to any material which might be effective to block the passage of air therethrough.)
In most commercial structures an air barrier membrane is used, usually made from a modified bituthane or a trowelled on modified bituthane or rubber. Sheet metal liners are also utilized in certain designs. Individually, these components have all been tested for effectiveness when purchased but a leakage problem may arise when these components are installed in a building system at the locations where these are joined to or abut different materials.
The standard location for the air barrier membrane is on the outside of the inside wall on the warm side of the insulation which is covered by the exterior finished facade. Therefore, the membrane is penetrated many times by ties and fastening systems including the insulation fastening system. Other building components such as windows are coupled together by means of the membrane and the junction between the membrane and window must be airtight to ensure that the overall air barrier (i.e. the building envelope) is effective.
Very little air pressure differential is required between the inside and outside environments separated by the building envelope to create an air leakage. The recommendation for allowed maximum leakage rate of building materials is 0.02 L/(s.m.sup.2) and for the building system is 0.1 L/(s.m.sup.2) at 75 Pa pressure as referenced in the National Building Code of Canada. A suitable testing procedure to test a building air barrier under maximum environmental air pressures would induce a pressure differential across the barrier of approximately 300 Pa in order to provide a test suitable for identifying leaks in the building system. For any structures where higher loads are expected, a maximum range of 1000 Pa to 2000 Pa would be utilized.
Testing systems for testing the effectiveness of air barrier and/or vapour barrier systems have been developed for use in a laboratory or other experimental setting in order to test the effectiveness of certain construction materials. An example of such testing apparatus is disclosed by U.S. Pat. No. 4,979,390 to Schupack et al which provides a vacuum apparatus used to test the porosity of a concrete structure and to identify any air leakages caused by cracks or fissures therein. However, building construction joins and other construction details are not capable of being tested by that apparatus at a building site because the Schupack apparatus is not capable of testing for air barrier continuity at the points of attachment of air barrier membranes (e.g. by means of ties and the like) or at the points of changes from one air barrier material to another. Moreover, the vacuum pressure required by the apparatus of Schupack far exceeds the foregoing air pressure differential levels to which the applicable building standards are directed. Some on-site (i.e. field) testing methods are available which use smoke tracers, infrared scanning techniques, air flow measurement devices, sound detection systems or tracer gas concentration detectors. However, the available on-site testing methods are not suitable for use during the on-going construction of a building and, instead, are intended for use after the completion of the building when corrective action is more difficult.
Therefore, there is a need in the construction industry for a means of testing for air leakages at any time during the construction phase, or in the laboratory, which may be conveniently and easily employed to simulate environmentally realistic conditions of air pressure differential across the air barrier according to accepted building standards. Further, there is a need for such a testing means for use on any type of air barrier whether it be the main building elements such as windows or an air barrier membrane (sheeting), or the various types of joints used in the building such as joints between walls, doors, windows, mechanical louvres, etc., insulation fastening systems, joins and laps in the air barrier sheeting, expansion and compression joints or masonry tie penetrations.
Vacuum testing systems are known for testing material strength and, in the case of U.S. Pat. No. 4,002,055 to Kops, for testing for leaks at seams between synthetic resin sheets. However, such vacuum systems are not suitable for testing building air barriers which cannot be successfully tested on site under vacuum conditions. The Kops apparatus utilizes a dome-shaped enclosure and a vacuum pump to create a very high pressure sufficient to pull overlapping resin sheets upward, at the seam between them, into the dome. Such a test is destructive by nature (since it operates by stressing the material being tested) and is not capable of testing joins between different construction materials on site.